Alright. poking around in the dark, I have found that the car DOES have a DRL module installed (Truck-Lite 97300) in that weird upside down fuse panel on the front drivers fender. I found that whoever had installed the kit had put in this cute little fuse breakout device, that plugs into an existing fuse slot and gives you a space for two fuses....one for routing back down to the factory fuse holder, and the other to a pigtail, which in this case was what was supplying power to the aftermarket relay module.
Turns out the reverse light fuse was blown.....for some reason. So I unplugged the DRL module fuse splitter, installed another 10A fuse in the original fuse slot, and lo and behold the reverse lights work again!
I currently have the DRL module un-powered. I THINK I have a better way to accomplish the always on marker lights, but I'll share that in a different thread.